The Phurnacite plant, methods of production
The manufacture of Phurnacite starts at the tipping blending site. The raw coals, fines, duffs etc are tipped and spread out in layers. The proportion of different coals being worked out at the laboratory.
Coals arrived form all over South Wales including the colleries listed below:
- Lady Windsor
- Tower Collery
- Merthyr Vale
Lady Windsor colliery, supplied approximately 3000 tons a week to the Phurnacite Plant. The layered coal is set into 4 separate dumps or pads. The Reclaimer, which really is a big roller with buckets inside of which is a conveyor belt, picks up the coal and feeds it onto the belts which conveys it to the bunker houses of either Number 1 or Number 2 plants. Coal is fed into the bunker house into large storage bunkers, about 200 ton capacity each.
The old method of blending coal was putting different coals into different bunkers and feeding off any proportion which is required. The diagram below shows the old method.
From the bunkers the coal is fed by means of a turntable onto a scraper conveyor belt to a bucket elevator, from where it is fed into a vertical dryer. This being a large steel tubular structure with shelves, feeding to the centre and out, with a central shaft with arms, which push the coal off the shelves.
A large furnace directs heat of approximately 600 degrees centigrade up through the dryer. The coal falling through this looses its moisture and comes out with only about 2% to 3% moisture left. This is then fed by means of conveyors and elevators, into dry bunkers.
A belt, which has a measuring system, feeds the required amount of coal into a cage mill. At the same time, pitch now in liquid form is pumped in at the required percentage (8%) to be mixed with the coal. After the grinding in the mill it is fed into a steam heated vessel called a “Pug” where it is further mixed and fed into a Worm conveyor or Screw conveyor, the amount of flow controlled by the press operator into the press where the rollers give about one and a half tons per square inch and Ovoids are formed.
Particle size of the coal at the press is very important. Generally, the finer the mixture, the denser the briquette but finer particles present a greater surface area and thus require more pitch, the most expensive constituent of the briquette. Therefore, the blend and quality and cost have to be considered. The denser Ovoids are sometimes difficult to lights and do not burn so well.
The raw Ovoids are fed onto a belt and cooled somewhat before going onto the Trammel Screens, which remove the fines and broken pieces. These are then returned at the plant to be reused. From the Trammel Screens the Ovoids are taken to the oven tops and they are fed into storage bunkers, corresponding to the ovens and batteries underneath, That is, 8 ovens in each block – 5 blocks to one battery. There are 40 Bunkers of approximately 2 tonne on each battery.
The pictures above all illustrate various stages during the method of production.